The variance effective size (Ne) was
formulated for populations of monoecious plant species that
are partly asexually propagating with discrete or
overlapping generations. It was shown that partly
asexually reproducing populations have larger or smaller
effective sizes (ratios to the census size N)
than fully sexually reproducing populations, according to
whether the term
Vc/c¯
is smaller or larger than the term
(Vk/k¯
+1−β)/2, where c¯ and
Vc are the mean and variance of
the number of progeny asexually produced per plant per year,
respectively, k¯ and Vk
are the mean and variance of the number of gametes contributed
per plant per year, respectively, and β is the selfing
rate of each plant. Asexual reproduction has no effect on
Ne when the two terms are equal, as is true when the
numbers of both sexually and asexually produced progeny per
plant per year are Poisson-distributed
(Vc/c¯=1 and
Vk/k¯=1+β).
Populations with a larger generation length (L) tend to
have a smaller effective size: for a population model of
age-independent survival and fecundity
with an annual rate δ of asexual reproduction,
Ne declines asymptotically to
N(2−β)/{3−β
+Vk/k¯
+(2Vc/c¯
−Vk/k¯
−1+β).δ} as L gets large, which
simplifies to N(2−β)/4
under a Poisson-distributed reproductive contribution. The
trade-off relation of Ne and L,
however, does not always hold: for stage-structured populations,
increase in the survival rate of
juveniles may act to increase both Ne and L.
Fixation and effective size in a haploid–diploid population with asexual reproduction
